The present invention is an improvement over the electric circuit breaker construction disclosed and claimed in U.S. Pat. No. 3,464,040, assigned to the assignee of the instant application. This patented construction provides a molded case circuit breaker of relatively narrow width, in practice, one-half inch wide, in answer to the demand for more compact circuit breaker load centers. Thus, utilization of half-inch wide circuit breakers in place of conventional one-inch wide circuit breakers affords a significant reduction in the load center size for the same number of branch circuits or, conversely, a significant increase in the number of branch circuits accommodated by a given load center size.
Unfortunately, with the reduction in circuit breaker width, the task of successfully interrupting short circuit currents becomes increasingly more formidable. This situation is further magnified by the current trend of electrical utilities to increase the "current available". The current available is the magnitude of current which potentially could flow in a circuit experiencing a short circuit. Whereas current availables of 5,000 amperes for residential electrical service were standard in the past, utilities are currently establishing current availables of 10,000 amperes and up for new installations. As a consequence, circuit breakers of higher interrupting capacity (IC) ratings must be installed. The current trend is to even higher current availables, calling for more expensive circuit breakers having higher IC ratings.
Interruption of such potentially higher short circuit current magnitudes places tremendous mechanical stresses on a circuit breaker. First, the circuit breaker must absorb the tremendous energies associated with interrupting the current flowing through its internal circuit. Secondly, in a two-pole circuit application, where one circuit breaker is side-by-side with another circuit breaker also endeavoring to interrupt the same short circuit current flowing in the opposite direction in its internal circuit, each must also withstand the forces exerted on its current carrying parts by the electromagnetic field associated with the current flow through the other. These forces have been known to dislodge parts of the circuit breaker and even impact them against the breaker case with rupturing force. Under these circumstances, even in the remote chance that the short circuit is successfully cleared, the circuit breaker is nevertheless irreparably damaged and must be replaced.
It is accordingly an object of the present invention to provide an electric circuit breaker of the above character wherein increased interrupting capacity is achieved without increasing the physical size of the circuit breaker.
Yet another object is to provide a circuit breaker of the above character, wherein increased interrupting capacity is achieved with only minimal, but nevertheless significant, structural changes to an existing circuit breaker design.
A further object is to provide a circuit breaker of the above character which is inexpensive to manufacture, and yet is efficient and reliable in operation.
Other objects of the present invention will in part be obvious and in part appear hereinafter.